Taharos, Chapter 1, Mishnah 8. Our mishnah continues to examine lumps of dough that cling to one another. Dough sticks, yet the pieces never fully merge: separate them and each one is once again its own lump. The mishnah here takes up the reverse of the more familiar case. Instead of tumah striking a cluster of lumps that were already joined, we have a single lump that already carries a level of tumah, and only afterward are fresh lumps of dough pressed onto it. What do the newcomers absorb while they are attached, and what remains of it when they are pulled away?
A lump that was a rishon
"Mikratzah shehaysah techilah vehishika lah acheiros, kulan techilah" - a lump of dough that was a rishon, and other lumps were pressed against it, they are all a rishon. As long as they are joined, the whole cluster is treated as one and shares the status of the original lump.
"Parshu, hi techilah vechulan sheniyos" - but when they are separated, the picture changes. The original lump is still a rishon, since it is the one that came into contact with the av hatumah. The others, however, drop back to being a sheni. They never touched the source of tumah itself; whatever they received, they received from a rishon, and that makes them a sheni. Their elevated standing lasted only as long as they were part of the joined mass.
A lump that was a sheni
"Haysah sheniyah vehishika lah acheiros, kulan sheniyos" - if the original lump was a sheni and other lumps were attached to it, all of them are a sheni while they remain joined.
"Parshu, hi sheniyah vechulan shlishiyos" - once separated, the original lump keeps its status as a sheni, and the attached lumps become a shlishi. From the perspective of what they held a moment earlier they have gone down a rung; from the perspective of the plain dough they were before they ever touched anything, they have of course gone up. Either way, they now stand exactly where dough touched by a sheni belongs.
A lump that was a shlishi
"Haysah shlishis vehishika lah acheiros, hi shlishis vechulan tehoros, bein sheparshu bein shelo parshu" - if the original lump of terumah dough was a shlishi and other lumps were pressed against it, it remains a shlishi and all the others are tahor, whether they were separated or whether they are still attached.
That they are tahor after separation is straightforward: terumah does not descend to a fourth level, so a shlishi has nothing left to transmit to them. Why they should be tahor even while they are still clinging to it requires more thought, and it is a matter of discussion among the commentators. According to the Bartenura and others, the reasoning runs as follows: since separating them would leave them completely tahor, their attachment cannot be counted as a genuine chibur, a true joining. And if it is not a real chibur, then even while they are pressed together they were never truly one body with the shlishi. They therefore remain tahor from beginning to end.
The mishnah thus draws a careful line. Attachment can lend a piece of dough a status it did not earn on its own, but only for as long as the attachment lasts, and only where the joining is meaningful enough to carry tumah in the first place.